This invention relates to an apparatus and method for monitoring an analyte.
Volatile compounds generated during food spoilage have conventionally been monitored by standard chemical laboratory methods. Volatile biological metabolites can be monitored to diagnose disease using similar methods. Assays have been developed to monitor the volatile compounds with improved accuracy, speed, sensitivity, selectivity and reduced cost. Some approaches to monitoring the compounds include electronic sensors, qualitative visual sensors, or analytical techniques such as gas-liquid chromatography.
Other approaches to protecting consumers from spoiled food rely on the appearance of spoilage molecules after passage of a predictable amount of time. For example, xe2x80x9cexpiration datesxe2x80x9d stamped on food containers, such as milk or juice containers, give consumers and indication of when spoilage might occur. The accuracy of the stamped dates depends on the history of conditions the food product is exposed to before consumption and is not dependable after the container is opened.
Another method of monitoring the potential quality of refrigerated, controlled-atmosphere-packaged and deep-frozen foods includes time temperature indicators, which monitor and indicate a possible unfavorable temperature history of refrigerated food. This approach typically does not provide specific information about the chemicals generated by the food product. Most consumer products rely on the combination of time stamps, food appearance, odor, and color to avoid spoilage.
A detector for monitoring an analyte includes an analyte-sensing composition. The analyte-sensing composition has a visible color intensity or emission intensity (e.g., fluorescence intensity) that changes as the analyte concentration contacting the detector changes. The intensity changes can be visible to the human eye, or identified by an instrument. The analyte can include carbon dioxide, a volatile amine or a volatile carboxylic acid.
In one aspect, a detector for monitoring a sample for the presence of an analyte includes a carrier, an analyte-sensing composition, a hydrophobic barrier, and an outer barrier. The carrier can be porous or fibrous. The analyte-sensing composition includes an indicator dye, a buffer, and an osmotic control agent and is contained by the carrier. The indicator dye can include an emissive dye, such as fluorescein complexon, or a colored dye, such as a phthalic acid derivative. The phthalic acid derivative can include o-cresolphthalein, phenolphthalein, or thymolphthalein. The hydrophobic barrier is on one surface of the carrier and is arranged to contact a test material. The hydrophobic barrier can include a hydrophobic silane coating, a fluorocarbon coating, or a laminated hydrophobic sheet. The outer barrier covers a surface of the carrier opposite the outer barrier. The outer barrier can be impermeable to water and gases. In certain implementations, the outer barrier can be transparent to visible light.
In another aspect, a method of detecting an analyte includes contacting the detector with a food product, body fluid or tissue and monitoring the detector for a change in visible color intensity or emission intensity from the indicator dye, which indicates the presence of the analyte. Monitoring can include detecting the change with an instrument or the human eye. The presence of the analyte can change the pH within the carrier. The method can include removing the detector from a sealed package prior to contacting the food product, body fluid or tissue.
In another aspect, a method of manufacturing a detector includes depositing a solution containing a solvent and the analyte-sensing composition on a carrier, removing the solvent, forming a hydrophobic barrier on a surface of the carrier; and placing an outer barrier on a surface of the carrier opposite the outer barrier.
In certain implementations, the detector can include a permeation modulator covering a portion of the hydrophobic barrier. The permeation modulator can have a lower permeability than hydrophobic layer or the carrier. The detector can be a portion of a food package or a hygiene product.
The details of the detector are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.